Welding type systems receive input power and provide welding type power. Welding-type system, as used herein, refers to any device capable of supplying welding type power, including ancillary devices such as a wire feeder, robot, etc. Welding type power, as used herein, refers to welding, plasma cutting or induction heating power.
Modern welding type systems includes power circuits and control circuits. Some components, particularly power components, need to be cooled. Such components are typically cooled using a fan blowing air across the component. Other components do not need cooling, and can have increased risk of failure if air is blown across them (particularly when the air is from a dusty or dirty environment, which is common where welding type systems are used). Thus, it is desirable to have some components subject to air flow, and others not subject to air flow.
Prior art welding type systems addressed the different air flow needs using an enclosed air flow space within the system housing. U.S. Pat. No. 5,642,260 (hereby incorporated by reference), issued to Sigl, and assigned to the owner of this invention, describes the first welding type system enclosed air flow space. U.S. Pat. No. 6,888,099, also incorporated by reference, describes another enclosed air flow space. These were commercialized and called the Miller® Wind Tunnel. Enclosed air flow space, as used herein, refers to a space within a welding power supply which provides air flow to components needing cooling, such as, for example, a Miller® Wind Tunnel. The Miller® Wind Tunnel provided for components that need cooling to be in the enclosed air flow space or windtunnel, and components that do not need cooling to be outside of the enclosed air flow space.
Printed circuit boards are potted to allow for more closely spaced components while maintaining a level of isolation between components. The potting also creates an environmental seal around these components, which reduces the likelihood of damage from dirt and debris when subject to air flow. One method of potting circuit cards is to place the entire assembly in a shell or cup and pot the entire assembly up to a specified level. Due to the cost of the potting compound, this can become expensive as the circuit card size increases.
Selective potting allows for a better use of potting compound, reducing cost and weight. Some circuit board assemblies require different environmental protection in different areas. For example, some components that need cooling are mounted on printed circuit boards with components that should avoid air flow. Prior art, such as the Miller® Dynasty® 280 Cooler Power Supply provided that portions of a circuit board in the wind tunnel were encapsulated in potting compound. The components that should avoid air flow are in the encapsulated region.
Many welding type systems have components with heatsinks, and only the portion of the boards with the heatsinks need to be exposed to the forced air flow. Also only the power section has high voltage components exposed that require extra protection. A significant portion of the board is less sensitive, low voltage control circuitry.
One prior art machine used a 5-sided cup that was molded and thru-hole components could be individually or group pre-potted in the cup. This reduced the amount of potting compound used, but is limited to thru-hole components. Also, the cup needs to be specific to the part that is being put in it since holes would need to be co-located with the pins of the component and sealed individually. This prior art had the potting compound poured into the cup, and not onto the board. When set, the potting compound was in the cup, and not on the board. This method did not allow flexibility in the location of components.
Another prior method uses dam-and-fill techniques to selectively pot components. The dam is formed by a high viscosity fluid and filled with a lower viscosity fluid. However, this method is limited in the depth of potting that can be achieved. This limitation is essentially the bead height of the damming material.
Another prior art technique is to use a potting tray. This requires the entire circuit card to be potted since it is placed in the shell. This can be costly and use more potting compound than necessary.
Another prior art technique is to pot the entire tray, except for the location of components that should not be potter, where voids were created with no potting compound. Each component that was not potted need a cap over it during potting to create the void. This wastes potting compound, since some areas that do not need potting were still potted, and was time consuming, since each component location that was not potted needed a cap.
Accordingly, a method of potting a circuit board in a welding type system that does not unnecessarily use potting compound, and is not time wasting, is desired.